A spring vice of this type has been known (DE 37 20 018 C2), which has two pressure plates, which have an approximately dish-shaped design. These pressure plates can be loosely inserted into the spring turns of a coil spring to be tensioned and can be tensioned in relation to one another by means of a spindle drive. The distance between the two pressure plates is reduced by the spindle drive during the tensioning process, so that the coil spring becomes shorter and is thus tensioned. This prior-art spring vice is designed as a telescopic coil spring, whose spindle drive has a threaded spindle with a spindle head having a key profile, which is mounted rotatably in a cylindrical guide tube via a thrust bearing. This guide tube has a radial contact surface for supporting the spindle head-side pressure plate. The threaded spindle can be screwed into a cylindrical threaded tube, which, axially displaceably, is in nonrotatable connection with the guide tube through positive-locking guide means. On the circumference of its end section located at a distance from the spindle head, the threaded tube has three radial fingers, via which the threaded tube can be brought into a nonrotatable pulling connection with the second pressure plate. To establish this nonrotatable pulling connection, the pressure plate has a central passage opening, in the edge area of which a corresponding number of locking recesses are arranged on the outside. On the side located opposite the locking recesses in the axial direction, the pressure plate has an approximately ring-shaped contact surface for accommodating a spring turn of the coil spring for tensioning this coil spring.
A radial expansion each is provided between two adjacent locking recesses in the circumferential direction, and the number of these radial expansions likewise corresponds to the number of the radial fingers. To make it possible to bring the threaded tube into nonrotatable pulling connection with the pressure plate, the threaded tube with its radial fingers is passed through the passage opening with its expansions and is rotated around the longitudinal central axis of the threaded tube to the extent that the radial fingers can engage the corresponding locking recesses belonging to them in a positive-locking manner when the threaded tube is moved toward the pressure plate in the opposite direction.
The radial fingers have an essentially wedge-shaped design. The locking recesses present in an equal number on the outside of the pressure plate located at a distance from the spindle head as well as the radial expansions of the passage opening located between two locking recesses each are countersunk with an oblique surface such that there is no flat contact surface for the radial fingers at least in the radial area of the radial fingers outside the locking recesses. It is ensured due to this special design of the locking recesses and of the radial expansions as well as due to the wedge-shaped design of the radial fingers that a pulling connection can reliably occur only when a nonrotatable positive-locking connection is formed at the same time between the radial fingers and the pressure plate. Thus, a slight rotation of the threaded tube after the passage through the radial expansions of the passage opening is sufficient to slide into the locking recesses during the movement in the opposite direction along the countersinkings having oblique surfaces.
The second pressure plate, which lies on the radial contact surface of the guide tube, likewise has a passage opening with radial expansions. These radial expansions are used to pass the spindle drive with the radial fingers of its threaded tube first through the second pressure plate and then through the first pressure plate from one side with the pressure plates inserted into the coil spring. The diameter of the passage opening is adapted to the guide tube and to the contact surface thereof and is made slightly larger than the passage opening of the first pressure plate. Furthermore, the second pressure plate has no locking recesses between the radial expansions, which locking recesses could be engaged by the radial fingers of the threaded tube in a positive-locking manner when the first pressure plate is replaced with the second pressure plate. This in turn means that if the two pressure plates are transposed by mistake, there is a risk that the radial fingers can slide off from the contact surface formed by the edge areas of the passage opening of the second pressure plate, so that a tensioned coil spring could be abruptly released in this case, which implies a considerable risk of injury to the operating personnel. Since this prior-art spring vice is designed as a telescopic spring vice, the spindle drive becomes shorter while the threaded spindle is being screwed into the threaded tube.
Another spring vice (Catalog of the firm of Klann Werkzeuge, 1994) has been known, which has essentially the same design as the above-described telescopic spring vice. This second spring vice differs from the telescopic spring vice by the design of its spindle drive. The spring vice has as the spindle drive a threaded spindle, at one end of which the above-mentioned radial fingers are arranged. A pressure cylinder or pressure piece is nonrotatably and axially displaceably guided on this threaded spindle. A thrust bearing, via which the pressure piece is supported at an adjusting nut in the axial direction, is provided in the pressure piece. The adjusting nut can be screwed onto the threaded spindle to tension a coil spring. Two pressure plates are likewise provided in this prior-art spring vice. The first pressure plate likewise has a central passage opening with locking recesses and radial expansions located between them in the circumferential direction.
The second pressure plate is likewise provided with a central passage opening with radial expansions, wherein the areas between the radial expansions of the passage opening form contact sections, with which the second pressure plate is supported at a radial contact surface of the pressure piece. This second pressure plate is guided with its passage opening centered on a cylindrical section of the pressure piece, which cylindrical section is arranged at the pressure piece on its end located opposite the thrust bearing and its diameter is smaller than the radial contact surface of the pressure piece. The diameter of the passage opening of the second pressure plate is adapted for guiding to the dimensions of the cylindrical section and is made correspondingly somewhat larger than the diameter of the passage opening of the first pressure plate.
This prior-art spring vice also involves a considerable risk of accident when the two pressure plates are transposed by mistake. This risk of accident results from the missing locking recesses of the second pressure plate, so that when the pressure plates are transposed, the radial fingers of the threaded spindle cannot engage the locking recesses in a nonrotatable, positive-locking manner, so that the radial fingers can slide off from the contact surface of the passage opening of this second pressure plate during the tensioning as well as the release of a coil spring. Even though an accidental transposition of the pressure plates can be recognized in a simple manner due to the different diameters of the passage openings of the two pressure plates, a transposition of the pressure plates may nevertheless happen, especially if a plurality of identical spring vices are used in the same plant and only the pressure plates without locking recesses of two spring vices are used together with a spindle drive of one of the spring vices to tension a coil spring.